The Internet has widely been used in recent years and users can access various types of information on sites operated all over the world and can obtain such information. Use of devices adapted to broadband access such as asymmetric digital subscriber line (ADSL) and fiber to the home (FTTH) has also rapidly spread accordingly.
IEEE Std 802.3ah™-2004 (NPD 1) discloses one scheme for a passive optical network (PON), which is medium-sharing-type communication in which a plurality of optical network units (ONUs) share an optical communication line and transmit data with an optical line terminal (OLT). Namely, NPD 1 defines Ethernet® PON (EPON), under which all information including user information passing through a PON and control information for administering and operating a PON is communicated in a form of an Ethernet® frame as well as an access control protocol (multi-point control protocol (MPCP)) and an operations, administration and maintenance (OAM) protocol for EPON. By exchanging MPCP frames between an optical line terminal and an optical network unit, joining, leaving, upstream multiple access control, or the like of an optical network unit is carried out. NPD 1 describes a method of registering a new optical network unit, a report showing a request for allocation of a band, and a gate indicating a transmission instruction based on an MPCP message.
In 10G-EPON standardized as IEEE802.3av™-2009 as well, that is, EPON in which a communication rate is adapted to 10 gigabits/second, which represents a next-generation technique for gigabit Ethernet® passive optical network (GE-PON) realizing a communication rate of 1 gigabit/second, an access control protocol is premised on the MPCP.
Japanese Patent Laying-Open No. 2010-267924 (PTD 1) discloses a laser drive circuit included in a transmitter in optical communication. The laser drive circuit includes a modulation circuit which supplies a modulated current to a laser diode in accordance with input burst data and a bias circuit which provides a bias current to the laser diode. The modulation circuit includes a differential drive circuit, and the differential drive circuit and the laser diode are AC coupled to each other by a capacitive element. In the differential drive circuit, a terminal resistance for impedance matching is connected between a pair of transistors and a power supply line.